Radio controlled pilot system



y .1947. F. L. MOSELEY 2,423,336

RADIO CONTROLLED PILOT SYSTEI Filed Feb; 10, 1941 4 Sheefs-Sheet 1 F. L.MOSELEY RADIO CONTROLLED PILOT SYSTEI July 1, 1947,

4 sheets-sheet 2 Filed Feb. 10, 1941 522mg W y 1947- F. L. MOSELEY 2,23,336

RADIO CONTROLLED PILOT SYS'I'EI Filed Feb. 10, 1941 4 Sheets-Sheet 3 3 vwwwbot Ma-SA. fi/aaelqy,

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July 1, 1947. MOSELEY, 2,423,336

RADIO CONTROLLED PILOT SYSTEII Filed Feb. 10, 1941 4 Sheets-Sheet 4PIT/l Patented July 1, 1947 UNITED STATES PATENT OFFICE RADIO CONTROLLEDPILOT SYSTEM Francis L. Moaeley, Chevy Chase, Md. aaalgnor t 8mm GmCompany. Inc. Brooklyn, N. Y., a corporation of New York ApplicationFebruary 10, 1941, Serial No. 378,296

:2 Claims. (Cl. 244-") The present invention relates to the automaticcontrol of aircraft, and particularly to the control of aircraft bysignals received from suitable remote radio stations located on theground.

It has heretofore been proposed to utilise positional signalstransmitted by radio statims for operating a position indicator locatedin an aircraft to give a pilot a visual indication of his position. Suchsignals are produced at the presout time by means of doubly modulatedtransmitters which define a plane of equal modulation. It is also knownto utilize a radio transmitter provided with a suitable antenna settingup a radiation pattern having a constant potential along a line suitablefor employment as a glide path registering through an indicator to guidea pilot in the landing of the aircraft. It has further been proposed toemploy a receiving loop stabilized in azimuth on the aircraft to definea course relative to a non-directional transmitter.

Any of the above or other radio transmission systems in conjunction withsuitable receivers, registering in the aircraft signals varying with theposition of the aircraft in space, is suitable for use in connectionwith the invention. I

employ the positional data derived from the radio signals to steer theaircraft automatically, without the agency of the pilot, on a flightpath coincident with the predetermined radio-defined course. Theinvention automatically corrects departures of the aircraft from thepredetermined course by suitably correcting the direction of theaircraft for returning the aircraft to the course.

It will therefore be understood that the primary object of thisinvention is to automatically steer an aircraft on a flight pathcoincident with a predetermined course defined by positional radiosignals.

A further object of the invention is to automatically correct departureof the flight path from the radio-defined course by directionalcorrections of an amount proportional to the departure.

A further object of the invention is to automatically correct lateraldeparture of the flight path from a radio-defined course by headingcorrections of an amount proportional to the departure.

A still further object of the invention is to automatically correctdeparture of the flight path from a radio-defined course by directionalcorrections proportional to the rate of change of position relative tothe course.

A further object of the invention is to automatically correct lateraldeparture of the flight 2 path from a radio-defined course by headingcorrections of an amount proportional to the rate of change of positionrelative to the course.

A further object of the invention is to automatically steer an aircraftover a flight path coinciding with a course defined by suitable radiosignals and varying in altitude.

Another object of the invention is to automatically correct verticaldeparture of the flight path from a radio-defined course by elevationcontrol corrections of an amount proportional to the departure.

Another object of the inventionis to automatically correct verticaldeparture of the flight path from a radio-defined course by elevationcontrol corrections of an amount proportional to the rate of change ofposition relative to the course.

A further object of the invention is to automatically bring an aircraftinto a landing over a flight path coinciding with a course defined bysuitable radio signals.

A further object of the invention is to automatically steer an aircraftthrough radio responsive control means operating automatic pilot meansin the aircraft.

A further object of the invention is to operate an aircraft steeringcontrol by an actuating motor in a proportionate manner withoutoverrunning.

A still further object of theinvention is to 0perate aircraft headingand elevational controls by actuating motors in a proportionate mannerwithout overrunning.

In carrying out these objects I provide a motor for controlling thedirection of the aircraft. This motor is controlled by a positionalsignal obtained from a radio receiver which varies in amplitudeaccording to the amount of departure of the aircraft from course.Normally this will be a small D. C. voltage, and in my system thispositional signal is opposed by a follow-up signal which measures thedirectional correction through which the aircraft is turned underoperation of the motor. When the directional correction is proportionalto the departure, the two signals will be equal and opposite and themotor will come to rest.

The positional signal obtained from the radio receiver is of the orderof a few microvolts and require great amplification in order to obtainproper actuation of the motor. In order to avoid the diificultiesinherent in direct current amplification I convert the D. C. controlsignals proportional to the departure of the aircraft from course and tothe directional correction under operation of the motor to A. C.previous to ampliflcation. If desired, the follow-up signal may beintroduced after conversion of the positional signal, in which case itwill be supplied as an A. C. voltage inverse in phase to the convertedpositional signal.

I prefer to employ a two phase alternating current motor in which onefield coil is energized by a local A. C. supply. The conversion of theD. C. signals to A. C. is carried out under control of the A. C. supplyso that the amplified signal will have the same frequency as the A. C.supply, and I provide means for causing the amplified signal to lead orlag the A. C. supply by 90. The amplifled signal is supplied to theother field coil of the motor. The phase inversion of the amplifiedsignal is dependent upon the polarity of the original D. C. signal andwill operate to control the direction of the motor.

As used in connection with a doubly modulated transmission system, theradio receiver output is constituted by two alternating current signalsof diflerent frequencies. These signals are separately rectified and theresulting D. C. potentials bucked against each other to produce aresultant D. C. signal proportional to the difference between theoriginal A. C. signals. I

Control systems operating as described may be employed for correctinglateral departures of the aircraft from a course by controlling theheading, and for correcting vertical departures from course bycontrolling the angle of climb or descent particularly for landingoperations. According to the invention a complete system will preferablybe provided for controlling the aircraft both horizontally andvertically.

The invention also contemplates automatically controlling the bank ofthe aircraft in dependency on the rate of turn.

In the specific embodiment to be described the heading and elevationcontrol systems are separately responsive to different radio signals butunder certain conditions where the aircraft is driven off course bothhorizontally and vertically may simultaneously operate to return theaircraft to course.

The inventive system will most conveniently be operated in conjunctionwith, and through the agency of, a suitable automatic pilot. Ordinarilysuch automatic pilot will be of the gyroscopic type and the radioresponsive control motor may perform its function of correcting thedirection of flight through one or more of the direction settingcontrols of the automatic pilot.

The operating principles of the invention, in regard to the horizontalcontrol of the direction, are broadly applicable to dirigible craft,such as surface craft.

This invention will be further understood in reference to the drawingsin which:

Fig. 1 illustrates the flight path of aircraft under my steering controldevice;

Fig. 2 represents a block diagram showing my invention applied to obtaincomplete automatic three-dimensional steering control of an aircraft;

Fig. 3 is a circuit diagram of my control device for the turn and bankcontrols of an aircraft;

Fig. 4 represents the signal and power supply circuits for the operatingunits shown in Fig. 3;

Fig. 5 is a circuit diagram of my elevator control device;

Fig. 6 represents the signal supply circuit of the operating unit shownin Fig. 5; and,

Fig. '7 is a diagrammatic representation of the operating relationshipbetween an automatic pilot and the control surfaces of an aircraft.

As shown in Fig. 1, the line AB represents in a horizontal planea coursedefined by positional radio signals. This course is produced in a knownmanner by the employment of doubly modulated radio transmitters to formradiation fields I and 2 of differing modulation frequencies. At thepresent time modulated frequencies of and cycles are employed. The tworadiation fields define a vertical plane represented as course AB inwhich the field strength of the two radiation fields are equal. Bysuitable circuits responsive selectively to the different modulationfrequencies used in connection with a radio receiver on an aircraft, itis possible to obtain a signal varying with the position of the aircraftrelative to its departure from course AB.

In order to control the flight path of the aircraft so that it willcoincide with the course AB it is necessary to establish in the aircrafta compass base line parallel in direction to the course AB, and tocontrol the flight path so that its deviation from the established baseline heading varies proportionately to the departure from the course.Assuming an arbitrary departure, the flight path of an aircraftcontrolled in this manner is represented by the path CD, in which thearrows represent the heading of the aircraft as it passes over theflight path. It will be noted that the heading deviation is large underlarge departure, and becomes progressively smaller as the flight pathapproaches the course. The amount of correction in heading may be suchas is required under operating conditions, and manifestly theproportionality need not be linear.

It has been found desirable in order to avoid hunting of the aircraftabout the course to provide a further control of the aircraft headingproportionate to its rate of change of position relative to the course.When this is applied in controlling the heading corrections of the planein addition to the correction proportional to the departure itself, theflight path of the aircraft under control of my invention is representedby a path E! of Fig. 1. It will be noted that because of the velocity ofthe aircraft in its return to the course it has been caused to assume aheading parallel to the course just previous to reaching the same. Thispermits the aircraft to attain an exact "on course" position through itscrosswise momentum, so that the aircraft does not overshoot the course.It will be noted that in the flight path CD the aircraft reached its oncourse" position with a slight cross-course velocity which would causethe flight path to overshoot the course by a slight amount. Whereas thedeparture resulting from overshooting the course would be immediatelycorrected, the necessity for this is avoided by employing a controlresponsive to the rate of change of the departure.

By utilizing a steering control responsive to the rate of change ofdeparture, it is also possible to obtain an accelerated correction ofheading when the aircraft suddenly departs from course because ofconditions encountered in flight. Because of the relatively largeheading correction in response to a quick departure, the amount of thedeparture is therefore minimized.

It will be understood that under operating circumstances wherein theflight path includes a drift component transverse to the direction ofthe aircraft caused by side winds, the direction of flight of theaircraft cannot be directly controlled itself because the driftcomponent depends on the magnitude of side winds which are notaccurately determinable. The flight path, however, is variable independency on the change of direction Masses of the aircraft andconsequently the desired iiis'ht path may in be attained through thedescribed directional corrections turning the aircrafttowardcourse.Therateof approach tothe couraedependsontheanglethroughwhichthe aircraftis turned, toward course. and therefore willlikewisevayinproportiontothe extentof departure. The control means operatingproportionallytothedepartureandtotherateofchange of departure operatesto compensate for drift by increasing the directional correction of theaircraftinprop rtiontoitsvelocityofdriftwhensuehdriftopposesitsreturntocourse, anddecreases the directionalcorrection when the drift is toward course, thereby substantiallymaintaining the desired direction of flight and ground course. 1

It will further be understood that the above principles of operation maybe carried out with any suitable source of positional signal for theaircraft and are in no way dependent on the specine radio systemdescribed. The same principles apply to the control of an aircraft in avertical plane in relation to a suitably arranged source of positionalsignals defining the desired course in respec to altitude. As a sourceof such a positional signal it is well known to employ either atransmitter setting up a radiation field having the desired coursedefined by a path of constant potential, or to use a doubly modulatedsystem operating to define a positional signal varying with altitude.The directional corrections are applied in the vertical plane to returnthe aircraft to course.

The manner in which my invention functions to carry out the propersteering control procedure to maintain the fiight path in coincidencewith the daired course may be described in connection with Fig. 2. Asshown therein, radio range receiver t is provided with antenna 6 forreceiving the doubly modulated radiation field described above. Thisreceiving system is well known, being utilized to operate the verticalneedle of the crosspointer instrument I for the purpose of giving thepilot a visual indication of his position relative to the course. Theoutput of the range receiver is utilized to operate the heading controlmotor 8. This motor controls the direction of the aircraft in ahorizontal plane through operation of the rudder. To obtain the desiredactuation of the rudder under control of motor 8 I contemplate the useof an automatic pilot in the aircraft, one such pilot being disclosed inPatent No. 1,992,970 of March 5, 1935, for Hydropneumatic automaticpilot.

This type of automatic pilot is well known in the art, but its operationis diagrammatically illustmied in Fig. 'l. The function of the automaticpilot in normal operation is to maintain the orientation of the aircraftconstant in space. This is accomplished under control of suitablegyroscopes described in the above noted patent which actuate throughservo-operated motors the control surfaces of the aircraft. Thus, asshown in Fig. 'l, rudder 9 is operated by motor ill under fluid pressurereceived from oil pressure lines ii. In order to obtain proportionateoperation of the rudder by the gyroscopic control mechanism, a follow-upconnection i2 is also employed. Similarly, ailerons I3 are operated bymotor I with oil pressure lines I and follow-up connection I 6.Elevators i! are similarly operated by motor is provided with oilpressure lines I! and follow-up connection". The operating mechanism isdescribed in detail in Patent No. 1,992,970.

Theautomaticpilotthusoperatestocontrolthe orientation of the aircraftabout the three principal axes simultaneousb. llanual control means arenormally provided for selecting the desired direction settings. Thus,heading control knob fl is provided for the directional gyropilot unit22 andisoperativetovarytheheadingoftheaircraft under the operation ofthe mic control mechanism. Similarly. bank control knob 23 of gyropilotIt is operative to select the desired angle of bank for the aircraftthrough operation of the ailerons II, and elevator control knob 2| isprovided to select the desired angle of climb or descent of theaircraft.

As shown in Pig. 2, motor 0 is provided with reduction gearing It and isoperatively connected to the heading control 2|. so as to control theheading of the aircraft through the desired operation of the rudder. Inorder to obtain a sumcient output to operate the turn control motor I, Iprovide turn control amplifier 21 for amplifying the output of the radiorange receiver.

In order to obtain a heading correction proportional to the departure ofthe aircraft, it is necessary to proportion the operation of the turncontrol motor I to the amplitude of the positional signal from the radiorange receiver. For this purpou it is convenient to employ apotentiometer 18 in the circuit shown with battery 29, adiustableresistance and center tapped resistance 3|. As shown. this potentiometeris operatively connected to turn motor I and functions to supply theturn control amplifier with a voltage proportional to the headingcorrection bucking the positional signal from the radio receiver. Undercontrol of this circuit turn motor 8 operates to change the heading ofthe aircraft only 'until the follow-up bucking voltage becomes equal andopposite to the positional signal, and thereby effects a headingcorrection proportional to the departure.

Although my turn control mechanism would operate in itself to return theaircraft to the vertical plane of the desired course, better control isobtained by effecting rigid turns free from skid by banking the aircraftin proportionto the rate of turn. For this purpose bank control-motor 32is provided, and is operatively connected through gearing 33 to the bankcontrol of the automatic pilot. In order to obtain bank in proportion tothe rate of turn I provide a'rate of turn measuring device It responsiveto the speed of turn control motor 8. The output from the rate of turnmeasuring device is amplified in the bank control amplifier 35 tooperate bank control motor 32. In order to obtain bank proportional tothe rate of turn, it is necessary that the operation of bank controlmotor 32 be proportional to the rate of turn signal, and for thispurpose I provide a potentiometer 35 similar in function topotentiometer 28. Potentiometer 36 is operatively connected to bankcontrol motor 32 and supplies a follow-up signal proportional to theangle of bank bucking the rate of turn signal. The amplitude of thefollow-up voltage increases in proportion to the operation of bankcontrol motor 32 and therefore causes motor 32 to bank the planeproportionately to the rate of turn.

In order to prevent over-running of the bank control motor, andconsequent huntin of the aircraft about the correct angle of bank, rateof bank measuring device 31 is provided for measuring the speed of bankcontrol motor 32. The rate of bank signal is introduced into the ba kcontrol amplifier to produce a positive braking action on bank controlmotor 32 as the inp t 818- nal, determined by thecombined rate of turnsignal and bank control follow-up voltage, approaches zero. Through thismean any tendency of the bank control motor to overrun the correctsetting is automatically checked and hunting is avoided. 1

In order to obtain automatic control of the aircraft in a vertical planea glide path receiver 30 with antenna 30 is utilized. As is well known,this receiver supplies a positional signal for operating the horizontalneedle of the cross-pointer instrument 1 in order to give the pilot avisual.

indication of his departure from course in altitude. I employ thissignal to control the altitude of the aircraft by the operation of motor40. Although the altitude control could be obtained through throttleoperation, I prefer to use motor 40 to operate the elevator control 25of the automatic pilot. For this purpose, motor 40 is provided withreduction gearing II and is operatively connected to the elevatorcontrol 25. Motor 40 is operated from the output of the glide pathreceiver 38 through elevator control amplifier 38.

In order to obtain a correction proportional to the departure inaltitude I provide follow-up potentiometer 42 operatively connected tomotor 40 for supplying a follow-up voltage proportional to the verticaldirectional correction bucking the glide path receiver signal 38.

For the purpose of preventing overrunning of motor 40 and consequenthunting of the aircraft, I provide speed measuring device 43 to obtain asignal proportional to the speed of motor 40 which is introduced intothe elevator control amplifier 38 so as to produce a positive brakingaction of elevator control motor 40 as the input signal from thecombined glide path receiver signal and the follow-up voltage approacheszero.

In each case the steering motor is controlled by a signal measuring thedisplacement from the desired direction, and by a follow-up signalmeasuring the amount of directional correction as the orientation of theaircraft is changed by operation of the motor. When the correction is ofan amount proportional to the deviation to be corrected the signals areequal and opposite, and no further operation of the steering motoroccurs until a further deviation takes place. Where desirable to preventoverrunning of the motor, its speed is measured, and if it is movingwhen the control signal and follow-up signal are equal, the speed signalpositively brakes the motor to a stop.

In order to measure the rate of departure from course a circuitcomponent may be employed which is responsive to the rate of change ofthe positional signal and operates to superimpose on the signal acomponent proportional to its rate of change. Such a device isdiagrammatically illustrated at 44 for the heading control and at I! forthe elevator control. When the rate of change measuring circuit isemployed, the directional corrections will be accelerated and increasedin proportion to the rate of change of departure to prevent overshootingon return to course and to minimize departure.

It should be mentioned that the operation of the invention has beendescribed in combination with commercially conventional receivers andfiight control instruments. These operating units are available for mypurposes in existing aircraft at th present time, and in such instancesmay be economically employed therewith, but it 8 is clear that theoperating principles of my system are independent of the particularunits de- Turn control circuit The control circuits for the turn controlmotor are shown in Figs. 3 and 4. In Fig. 4 is diagrammaticallyillustrated radio range receiver 5 which is responsive to the doublymodulated radiation field illustrated in Fig. 1. The radio rangereceiver separates the two modulating frequencies and provides a dualoutput. The output signals constitute alternating currents of therespective modulations of the field pattern, and are proportional totheir respective amplitudes at the loca tion of the aircraft in space.The output signals are amplified by tuned amplifiers I and II which arecoupled to a rectifier network 50 by transformers 48 and 59. M is wellknown, the rectifier network produces a direct current signalproportional to the relative strengths of the mod lation frequencies ofthe field pattern, varying .in sign in dependency on which modulatingfrequency predominates, and falling to zero where the field strengthsare equal. In this way a sigmanner, and in my system is utilized toprovide the basic control for the turn motor I. For this purpose. thesignal from the rectifier network 50 is led to terminals 5| which areconnectable with the signal input terminals 52 of the turn controlamplifier as shown in Fig. 3. Low pass filter III is provided to removeresidual components of the modulating frequencies which may betransmitted through the rectifier network.

As shown in Fig. 4 I also provide a power supply for the turn controlmotor comprising vibrator 53, transformer 54 and rectifier II. Thissupplies an alternating current output to terminals 56, and, throughchoke coils 51 and condensers 58, direct current at terminals 59 and I.

The alternating current supply from terminals '58 is connected toterminals SI of the turn control amplifier, and the direct current fromterminal ill is connected to terminal 82. The power supply and amplifierare provided with a common ground circuit.

The turn signals from terminals I! are connected through switch I toconductors N and II. Conductor 84 is connected to conductor '0 throughcenter tapped resistance ii and potentiometer 28, the operation of whichwill be hereinafter described. Conductors 6! and 86 are connected toterminals '1 and 68 of vibrator II. This vibrator comprises contactpoints II and H, and vibrating blade 12 which is actuated by magnet coil18. The output from the vibrator is fed to the center tapp d Primary llof transformer II. The magnet coil of the vibrator is connected to thealternating current source through conductors II and TI and half-waverectifier ll. Consequently vibrator blade 12 is actuated by theresulting current pulses to produce an alternating current intransformer II of a frequency equal to the alternating current supply,and of an amplitude proportional to the direct current input to thevibrator. The vibrator constitutes in efiect a modulator.

Transformer 1! is provided with secondary II masses 9 which is connectedto control grid 88 of the first turn amplifier tube 8|. Condenser 82 isplaced across the secondary of transformer 18 to improve the waveform ofthe alternating current generated by the vibrator.

The turn control amplifier constitutes a conventional system employing,in addition to the input tube 8|, resistance coupled tubes 88 and 88which feed through transformer 88 push-pull tubes 88 and 81. Tubes 88and 81 are connected to the split primary 88 of output transformer 88.Primary 88 is shunted by condenser 88 to provide further improvement inthe waveform.

The secondary ll of transformer 88 couples the amplifier output to fieldcoil 92 of the turn control motor 8.

Turn control motor 8 is also provided with field coil 88 which is fedthrough conductors 84 and 88 by the alternating current supply.

As shown, motor 8 constitutes a two-phase motor which is operated by thealternating current source and the alternating current gener-' ated bythe vibrator from the direct current positional signal. It will beunderstood that due to the dependency of the actuating coil of thevibrator on the alternating current supply, the alternating currentgenerated by the vibrator maintains a definite phase relation with thealternating current supply. It will also be understood that thealternating current generated by the vibrator will shift its phase by180 in response to a reversal of direction of the direct current signal.The circuit constants of the turn control amplifier are so adjusted thatthe output thereof as nearly as possible leads or lags the alternatingcurrent by 90. Consequently, motor 8 will operate in dependency on thedirect ourrent input to the vibrator, and will respond to a reversal inpolarity thereof by a reversal in its direction of rotation. Y

Turn motor 8 is operatively connected to the heading control of theautomatic pilot, as described in connection with Fig. 2. The operationof the heading control causes a heading variation of the aircraft whichis directly proportional to the movement of the heading control.

Operation of the turn motor 8 actuates potentiometer 28 to set up avoltage between conductors 88 and 68 as the contact arm moves relativeto the midpoint of the resistance element. The potentiometer is suppliedwith the desired voltage gradient by means of battery 29 and rheostat88. The voltage set up by the potentiometer is in direct proportion tothe actuation of the heading control, and consequently this voltage is ameasure of the deviation in heading caused by operation of turn motor 8.It will therefore be understood that operation of turn motor 8 isinaugurated on the appearance of a positional signal at terminals 52indicating a lateral departure of the aircraft from its course, and thatthe turn motor continues to operate to change the heading for returningthe aircraft to course until the voltage set up by potentiometer 28balances out the positional signal, that is, until the heading corretionas measured by this voltage is equal to the departure as measured by thepositional signal voltage at terminals 52. In this way the followupvoltage fromthe potentiometer acts to proportion the heading correctionof the aircraft to its departure from course, and thereby causes theaircraft to correct its departures by a flight path such as shown at CDin Fig.1. The flight path for correcting departure is under control ofthe output from potentiometer 28 which is determined by the inputvoltage supplied thereto, and by the type of winding, which may belinear or non-linear as required. It will be understod that the headingcorrection is continuously diminished as the aircraft approaches coursein accordance with the diminishing position signal at terminals 82.

Manual control of the aircraft may be obtained through my device byoperation of switch 88 to interconnect conductors 84 and 88, whereuponthe control signal for the turn control motor is obtained from thefollow-up potentiometer 28. The motor therefore runs to restore thesystem to balance and in so doing changes the heading of the aircraft.

To employ this action control knob I" is provided connected topotentiometer 28 by gearing "8. Operation of knob I'll rotatespotentiometer 28 relative to turn motor 8 by slipp of friction clutchI15. Motor 8 immediately responds to the output from the potentiometercircuit resulting from movement of the potentiometer from balanceposition, and operates to change the heading until the potentiometer isreturned to balance.

The amount of heading change under manual control will be proportionalto the rotation given control knob I11, and consequently the settin ofthe automatic pilot may be controlled hereby. This is particularlyuseful when employed in connection with the automatic bank control to bedescribed below.

In order to obtain a heading correction proportional to the rate atwhich the aircraft is approaching or leaving the course, I may employcircuit means responsive to the rate of change of the positional signal.As shown in Fig. 4, these may comprise an inductance 88 shunting thereceiver output, and resistor 8'I and condenser 88 which are in parallelto each other and in series with the receiver output. If the directcurrent signal increases from a steady state the reactance temporarilyassumes a high resistance to the increasing current and thereforeincreases the output voltage proportionately beyond what it would be inthe steady state. Simultaneously condenser 88 effectively shuntsresistor 81 for the rising current and additionally increases the outputto terminals ii. In effect, therefore, the rate responsive circuitsuperimposes on the receiver output a signal component proportional toits rate of change, and thereby increases the heading correction. i

Similarly, in response to movement of the aircraft toward course thereceiver output drops, and inductance 96 generates a self-inducedcurrent of reverse polarity which further reduces the voltage atterminals 5|. At the same time a decreasing voltage is set up overresistance 81 and condenser 88 immediately producing a voltage furtheropposing the receiver output. In this way, a component proportional tothe rate of decrease of the positional signal is superimposed thereupon,and the heading correction of the aircraft is decreased in dependency onthe rate of approach to course.

In the input circuit shown, a the follow-up potentiometer and thepositional signal source are in series, the rate responsive circuitcomponents also superimpose a component on the circuit proportional tothe rate of change of the potentiometer output.

The turn control motor operates under the basic control of a positionalsignal proportional to departure from course. The basic signal is trans-11 formed to an alternating current having the irequency of a locallygenerated A. 0. supply, is ampliiied, and is utilized with the locallygenerated A. C. supply to actuate the turn control motor. The change oiheading oi the aircraft under operation of the turn control motor isalso measured by a follow-up signal which opposes the positional signal.In the iorm shown the iollow-up sllnal is constituted by a D. C. voltageopposing a D. C. positional signal, and the polarity of the resultingvoltage determines whether the amplified A C. signal leads or lags thelocal generated A. 0. pp y.

In the embodiment shown wherein the positional signal is derived from adoubly modulated radiation system it first appears as two alternatingcurrents oi. different frequencies which are transformed to analternating current of the frequency of the locally generated A. C.supply through rectification to a single direct current signal which isthen converted to A. C. under control of the locally generated A. C.supply.

Circuit components have also been shown for superimposing on thepositional signal a component proportional to its rate of change.

Bank control circuit It is desirable, in order to avoid side-slip oi theaircraft, to bank the same in proportion to the rate of turn. It will beunderstood that under operation of the automatic pilot heading controlthe heading is changed by a constant amount for each revolution of turnmotor 8. In order to determine the rate of turn of the aircrait it istherefore convenient to measure the speed oi turn control motor 8, andto bank the plane in proportion to this speed.

For this purpose I provide an inductance-resistance bridge comprisingileld coil 02 oi the turn motor 8, and resistance I02 as one pair ofarms, and inductance 99 and resistances I and IM as the other pair. Thisbridge is balanced by rotating the motor manually to provide an inputvoltage for the turn control amplifier through operation ofpotentiometer 28, and the motor is then blocked in this position. Thetotal value of resistances I00 and MI is then adjusted until the phaseangle of the voltage drop across these resistances is the same as thedrop across resistance I02. The relative values oi resistances I00 andNI are then adjusted without changing their total value so that thevoltage drop across resistance I M is exactly equal and opposite to thatdeveloped across resistance I02. When the turn motor 8 is allowed torotate, the inductance of field coil 92 will increase proportionately tothe rotation, and an unbalance voltage proportional to its speed will besupplied to conductors I03 and I04. This speed signal will be oi airequency equal to the alternating current supply, of anamplitudeiproportional to the speed oi turn control motor 8, and willreverse its phase through 180 in dependency on reversal oi turn motor 8.The speed signal constitutes a basic control for bank motor 32 which isoperatively connected to the bank control of the automatic pilot andwhich thereby varies the bank oi the aircraft.

The output of the turn motor speed bridge is connected in series withpotentiometer 30 which receives an alternating current supply throughconductors I05 and I08. The potentiometer II is shunted by center tappedresistor I01. Potentiometer 36 supplies an alternating iollow-up signalof an amplitude proportional to the displacement of the potentiometerirom its center position and undergoing a phase reversal oi 180 as thepotentiometer arm passes irom one side to the other side oi the centerposition. 0onsequently. the output oi iollow-up potentiometer It may becaused to oppose the output irom the turn motor speed bridge by suitablephase shiiting means inserted in its supply circuit. For this purpose Iprovide condenser I and inductance I00.

In order to prevent overrunning oi the bank control motor I! I providemeans ior measuring its speed, which becomes operative to supply aninput control voltage ior the bank motor to brake it, should it overrunthe primary control signals constituted by the voltages irom the turncontrol motor speed measuring device and the bank motor iollow-uppotentiometer. This is constituted by a speed responsiveresistance-inductance bridge comprising ileld coil II! oi the bankcontrol motor 32, inductance III, resistance III, and resistances IIIand Ill. The output of this bridge and its operation provide a signalmeasuring the speed oi the bank control motor similar to the speedmeasuring bridge ior turn control motor 8.

The output oi the bank motor speed measuring bridge is also proportionalto the rate oi change 01' the output of the bank control motor iollowuppotentiometer circuit, and to the rate oi change oi bank caused byoperation oi the bank control motor.

The bank control amplifier is constituted by resistance coupled tubesII! and I It, which ieed push-pull tubes Ill and H0. Input transiormerII! is provided for the amplifier, and includes secondary I20 ieedingthe grid of the input tube II! and shunted by condenser IZI to improvethe A. C. waveiorm. The push-pull output tuba II! and H0 feed centertapped primary I22 oi output transformer III which is shunted bycondenser I24 also to improve the A. C. waveiorm. Output transformer I23is provided with secondary I25 for matching the impedance oi field coilIIO oi the bank control motor. This motor is also provided with fieldI20 excited by the local A. C. supply through conductors Ill and I28.

The primary I28 oi input transformer II! is included in the bank motorcontrol circuit which comprises the turn control motor speed measuringbridge, the bank control motor iollow-up potentiometer, and the bankcontrol motor speed measuring bridge, all connected in series.

The bank control motor operates under a signal comprised oi a componentproportional to the speed of the turn control motor, a componentproportional to the bank of the aircrait under operation of the turncontrol motor and bucking the turn motor speed component, and a thirdcomponent proportional to the speed oi the bank control motor buckingthe resultant of the first two components.

The operation oi the bank control motor speed measuring bridge is bestconsidered in comparison to the operation of the bank control motorwithout the bridge. In such a circuit the bank control motor wouldrespond to a signal measured by the diiierence in output between theturn control motor speed bridge and the bank control motor follow-uppotentiometer. As the resultant signal varies the bank control motorwould tend to overrun as balance is reached, due to its momentum.Overrunning is particularly objectionable because it would result inhunting about the proper bank angle a the operation oi the bank controlmotor carries the bank iollowup potentiometer through the balancingposition.

In order to prevent overrunning or the bank control motor through theposition of zero signal resulting from the combined outputs of the bankfollow-up potentiometer and the turn control motor speed measuringbridge, the bank control motor speed measuring bridge is employed. Thisproduces a signal proportional to the speed of the bank control motorwhich operates to oppose the signal otherwise supplied to this motor bya potential proportional to the speed of this motor. In case the motorshould overrun on a decreasing signal an increased voltage will besupplied from the speed measuring bridge which will additionally opposethe signal otherwise supplied and reduce its effective value. The outputfrom the speed measuring bridge may include a component produced by theback E. M. F. from the bank control motor on overrunning. As the signalotherwise supplied approaches zero, the speed responsive component will,in case of overrunning, assume relatively thereto a large value and mayactually exceed the other signal to supply a reverse effective signalwhich positively brakes the bank control motor. In any case where thespeed control motor i moving to produce a signal from the speed bridgecircuit, if the signal otherwise supplied is zero, the speed bridgesignal will supply a braking E. M. F. through the bank motor amplifierto the bank control motor which immediately arrests its movement. Inthis way the movement of the bank control motor is immediately arrestedwhen the turn control motor speed measuring bridge and the bank controlmotor follow-up potentiometer have equal and opposite outputs.

Elevator control circuit The operating circuits for the elevator controlmotor 40 are shown in Figs. and 6. The operation of this motor is inmany respects similar to that of the turn control motor.

The positional information for controlling the vertical flight pathcomponent is derived from a glide path receiver 38. As is well known,this receiver is utilized in connection with a radio transmitter havinga radiation pattern providing a path of constant intensity along whichthe aircraft is guided. The course defined by the glide path transmitteri utilized to bring the aircraft into a landing. The glide pathtransmitter is modulated at an audio frequency.

As is usual, the output from the glide path receiver is rectified andoperates the horizontal needle of the crosspointer instrument I as shownin Fig. 6. The receiver supplies a small D. C. voltage which isgenerally dependent upon the altitude of the aircraft. Low pass filterI82 is propath receiver and is shunted by battery I85 and vided toremove frequency component which might interfere with the operation ofthe elevato control motor. When the aircraft is on the desired coursethe output of the receiver has a definite value, and when the aircraftdeparts vertically from the course the receiver output increases ordecreases in dependency on themrection of the departure. This outputfrom the glide path receiver is supplied to terminals I 3| and I32 asshown in Fig. 6 which are connectable with the input terminals I 33 andI34 of the elevator control circuit shown in Fig. 5. In order to obtaina positional signal which reverses its sign in dependency on which sideof the course the aircraft is, I provide resistance I35 connected toterminal I34, This resistance is in series with the output circuit fromthe glide rhecstat III. The current from battery Ill is employed to setup a potential over resistance I opposing the output from the glide pathreceiver so that the efiective input to the elevator control circuitwill be zero when the aircraft is on course, and which will change itssign depending upon whether the aircraft is above or below the course.

These circuit components in combination with the glide path receiversupply the elevator control amplifier with a positional signal entirelysimilar to that supplied the bank control amplifier by the rectifiedinput from the range receiver. The elevator control motor 45 similarlyoperates potentiometer 42 to supply a follow-up voltage in combinationwith battery I35, rheostat I39, and center tapped resistor I40. Theresultant signal from the combined position signal and follow-up voltageis supplied by conductors I4! and I4! to vibrator arm I43 which isoperated by actuator coil I44 energized by the A. C. supply fromterminals I45. The A. C. supply is rectified to form a series of pulsesfor operating the vibrator I43 by half wave rectifier I48. Thus the D.0. signal is modulated at the frequency of the A. C. supply.

The elevator control amplifier receive its input through transformer I41and comprises resistance coupled tubes I48, I49 and I50 an pushpulioutput tubes III and I52. Its output is coupled to field coil I53 oi theelevator control motor by transformer I54. The other field coil I55 ofthe elevator control motor is energized by the A. 0. supply th'roughconductors I56 and Ill.

The operation of this amplifier is in all respects similar to that ofthe turn control amplifier, with the exception of the operation of theelevator control motor speed measuring bridge which includes field collI53 and resistance I5l as one pair of. arms and inductance I50 andresistances I50 and iii as the other pair. In

order to prevent hunting of the aircraft about the cours defined by theglide path transmitter, the output from this speed measuring bridge isintroduced into the elevator control amplifier at control grid I62 oftube I49. The function of this speed responsive signal is in allrespects similar to that of the signal produced by the bank motor speedbridge, and it therefore prevents overrunning of the elevator controlmotor 45 and consequent hunting.

As described in connection with Fig. 2 the elevator control motor isoperatively connected to the automatic pilot and by operation thereofcontrols the angle of climb or descent of the aircraft. 'Ih'edirectional correction in the vertical plane caused by operation of theelevator control motor 40 is measured by the output from follow-uppotentiometer 42 operated by the motor and the input to the elevatorcontrol amplifier becomes zero when this voltage is equal and oppositeto the positional signal measuring the vertical departure from course.Th elevator motor speed measuring bridge is effective to preventoverrunning of the motor and hunting of the aircraft about the desireddirection in the vertical plane.

In order to accomplish directional corrections proportional to the rateof change of departure in a vertical direction from course, I employcircuit components for superimposing on the positional signal acomponent proportional to its rate of change. These ar illustrated inFig. 6, and for the purposes of illustration a diflerent circuit has 15been shown from that employed with range receiver I for' controlling theheading of the aircraft.

The output from the glide path receiver is connected by conductors I andIll to a bridge circuit comprising resistances ill and I" and mutuallycoupled inductances I and I". The output from the bridge circuit issupplied to terminals iii and in through conductors I'll and "I. It willbe understood that in a steady-state condition induotances I" and illeflectivcly shunt .the output received at terminals Ill and III,

but that they oppose a proportionately increasing resistance on a risingsignal to increase the output relative to their action in a steady-statecondition; and generate an opposing voltage on a decreasing signal toreduce the output relative to their action in a steady-state condition.The bridge therefore superimposes on the positional signal a componentproportional to its rate of change, and the resulting signal supplied atterminals Iii and I3! causes .the elevator control motor to correct thedirection of the plane in proportion to the rate of change of departurin the vertical relative to the course deflned by the glide pathtransmitter.

It will be understood that in landing the automatic vertical control ofthe aircraft should be immediately terminated on contact of the aircraftwith the ground either automatically or by a manual control operable bythe pilot. For this purpose switch I18 is provided in conductor ii! fordeenergizing the fleld coil III of the elevator control motor 40.

In accordance with the above description it will be understood that theinvention contemplates the completely automatic control of the flight ofan aircraft in dependency on positional information derived from radiosignals. Under operation of my system the aircraft is automaticallyguided to maintain the desired course. The system is similarly designedto automatically land an aircraft, which operation is automaticallycarried out without requiring any manual control dependent upon thepersonal Judgment of the pilot.

Whereas it is desirabl to employ the complete system, under certaincircumstances only certain components thereof need be utilized. Forinstance, my turn control unit either with or without the bank controlunit may b employed in instances where it is unnecessary to maintain anautomatic control of the altitude of the aircraft. Similarly, thealtitud control unit may be used alone, where automatic control of turnand bank of the aircraft is not desired. It is clear that the operatingprinciples of my system are not restricted in any way to the speciflccircuits described, but may be utilized in other embodiments.

Divisible portions of the invention or inventions hereinbefore describedhave been made the subject of a later application constituting acontinuation-in-part of the present application, Serial No. 444,395,flied May -25, 1942, for Radio controlled pilot system, and a divisionalapplication Serial No. 505,917, flied October 12, 1943, for Radiocontrolled pilot system.

I claim:

1. In an aircraft flight control system, in combination, automatic pilotmeans for steering the aircraft in a desired direction, control meansfor the automatic pilot means operative to cause the automatic pilot tochange the direction or the aircraft, means for deriving a controlpotential varied by the rate of change of departure of the aircraft froma desired path of travel, and actuating means for the automatic pilotcontrol means operative in dependency on said control potential to turnthe aircraft toward course by an angle depending at least in part on therate or change of departure from course.

2. In an aircraft flight control system wherein a signal voltageproportional to the position of said aircraft relative to apredetermined flight path is produced, electromagnetic actuating meansfor causing operation of said steering control means, aircraft steeringcontrol means, a control circuit for said actuating means adapted toreceive said signal for controlling the electromagnetic actuating means,means responsive to said signal voltage adapted to produce a componentthereof proportional to the rate of change of said signal voltage, andcircuit means connecting with the control circuit operative tosuperimpose on the signal voltage said component proportional to therate of change of the signal voltage.

3. In an aircraft flight control system wherein a. signal voltagevarying proportionally to displacement of said aircraft from a desiredpath of travel is produced, aircraft steering control means,electromagnetic actuating means for operating said aircraft steeringcontrol means, a control circuit for said actuating means adapted toreceive said signal voltage, means responsive to said signal voltageadapted to produce a component thereof proportional to the rate ofchange of said signal voltage, and circuit means connecting with thecontrol circuit operative to superimpose on the signal voltage saidcomponent proportional to the rate of change of the signal voltage.

4. An actuating device for controlling an aircraft automatic pilot toreturn the aircraft to a. desired flight path including electricalcircuit means adapted to receive a positional signal from a radioreceiver proportional to the departure of the aircraft from the desiredflight path deflned by said signal, means responsive to the rate ofchange of the positional signal in said circuit, and actuating means forcontrolling said automatic pilot operating in dependency on the lastmentioned means in response to the rate of change of the positionalsignal to cause the automatic pilot to turn the aircraft toward thedesired course through an angle depending at least in part on the rateof departure of the aircraft from the desired flight path.

5. In a system for automatically steering a dirigible craft to follow apredetermined course deflned by radio signalling, means operable inresponse to said signalling, means controlled by said signal responsivemeans proportionally to the rate of change of position of said craftrelative to said course, and means actuated at least in part by saidlast-named means connected to correct departures or said craft from saidcourse.

6. In a flight control apparatus for automatically directing a craftalong a predetermined path deflned by a radio signal, means at saidcraft responsive to said signal, steering controls on said craft, andmeans connecting said signal responsive means to actuate said steeringcontrols to maintain said course by directional corrections proportionalto the extent of departure from said course, said last-named means beingresponsive to the extent of departure of said craft from said course andto the rate of change of said departure.

7. In a flight control apparatus for automatically steering an aircraftalong a predetermined course defined by radio signalling, means at saidaircraft responsive to said signahheading control means on saidaircraft, and means connecting said signal responsive means foractuating said heading control means to return said aircraft to courseby directional corrections proportional to the extent of saidlateraldeparture and to the" rate of departure from said course.

8. In a control system for steering a craft relative to a course definedby a radio signal comprising two components of different characteristieon either side of said course. a receiver on said craft responsive tosaid signal and adapted to produce a dual alternating current outputcorresponding to said components, rectifying and mixing means comparingsaid dual output components to provide a direct current signalproportional in amplitude to the relative strengths of said components,means converting said direct current ignal to a proportional alternatingcurrent signal, means operative in response to a change in polarity ofthe direct current signal resulting from displacement of said craft toone side or the other of said course, to shift the phase of saidconverted signal, and motor means operated by said converted signal,said motor means being responsive to said phase shift for determiningthe direction of operation of said motor means.

9. In a control system for automatically steering an aircraft along anequal intensity path created by radio waves forming partiallyoverlapping radiation patterns in space, automatic pilot means forstabilizing said aircraft on an adjustable heading, radio receivingmeans responsive to said radio wavesfor producing a control signalhaving an amplitude substantially proportional to the difference inintensity of said radiation patterns at said aircraft, and turn controlmeans actuated by said receiving means for changing the heading of saidaircraft by an angle proportional at least in part to theamplitude ofsaid control signal to maintain said aircraft on said equal intensitypath.

10. In a control system for automatically directing an aircraft along apredetermined line of flight defined by directively' radiatedelectromagnetic energy, automatic pilot means for stabilizing thelongitudinal axis of said aircraft at an adjustable pitch angle, radioreceiving means responsive to the intensity of said radiated energy forderiving a pitch signal having an amplitude which is a measure ofdisplacement of said aircraft from said predetermined line of flight,and means responsive to said signal for changing said adjustable pitchangle by an angle dependent upon the amount of said displacement todirect' said aircraft back to said predetermined line of ht.

11. In a control system for automatically directing an aircraft along apredetermined line of flight defined by directively radiatedelectromagnetic energy, automatic pilot means for stabilizing thelongitudinal axis of said aircraft at an adjustable pitch angle, radioreceiving means responsive to the intensity of said radiated energy forderiving a pitch signal having an amplitude which is a measure ofdisplacement of said aircraft from said predetermined line of flight,means for deriving a rate of pitch signal from said receiving meanscorresponding to the rate of displacement of said aircraft from saidpredetermined line of flight, and mean actuated 18 by said pitch andrate of pitch signals for changing said adjustable pitch angle by anangle dependent upon the magnitudes of said signals to direct saidaircraft back to said predetermined line of flight.

12. In a control system for automatically steering an aircraft along anequal intensity path defined by partially verlapping radiation patterns,automatic pilot eans for stabilizing said aircraft on an adjustableheading, radio receiving means responsive to the relative intensities ofsaid radiation patterns for developing a signal representative oflateral departure of said aircraft from said equal intensity path, andmeans responsive to said receiving means for'adjusting the heading ofsaid aircraft through an angle dependent upon the magnitude of saidlateral departure to return said aircraft to said equal intensity path.

13. In a control system for automatically steering an aircraft along anequal intensity path de-' flned by partially overlapping radiationpatterns, automatic pilot means for stabilizing said aircraft on anadjustable heading, radio receiving means responsive to the relativeintensities of said radiation patterns for developing a turn signalrepresentative of lateral departure of said aircraft from said equalintensity path, means for deriving a rate of turn signal from saidreceiving mean representative of the rate of lateral departure of saidaircraft from said equal intensity path, and turn control means actuatedby said turn and rate of turn signals for adjusting the heading of saidaircraft through an angle dependent upon the magnitude of said signalsto return said aircraft to said equal intensity path.

14. In a control system for automatically directing an aircraft along apredetermined line of flight defined by directively radiatedelectromagnetic energy, automatic pilot means for stabilizing an axis ofsaid aircraft, radio receiving means responsive to the intensity of saidradiated energy for deriving a signal having an amplitude which is ameasure of displacement of said aircraft from said predetermined line offlight, and means responsive to said receiving means for rotating saidaxis, through an angle dependent upon the amount of said displacement todirect said aircraft back to said predetermined line of flight.

15. In a control system for automatically steering an aircraft along anequal intensity path created by radio waves forming partiallyoverlapping radiation patterns in space, automatic pilot means forgyroscopically stabilizing an axis of said aircraft, radio receivingmeans responsive to said radio waves for producing a control signalhaving an amplitude substantially proportional to the difference inintensity of said radiation patterns at said aircraft, and meansresponsive to said receiving means for rotating said axis through anangle dependent at least in part upon the amplitude of said controlsignal to maintain said aircraft on said equal intensity path.

16. In a control system for automatically steering an aircraft along anequal intensity path deflned by partially overlapping radiationpatterns, automatic pilot meansfor stabilizing said aircraft on anadjustable heading, radio receiving means responsive to the relativeintensities of said radiation patterns for developing a signalrepresentative of lateral departure of said aircraft from said equalintensity path, means controlling the heading on which said aircraft isstabilized, and means for producing a signal dependent upon angulardeviation of said aircraft from a predetermined heading, said controlmeans being responsive to said signals for changing said aircraftheading an amount sufficient to balance said signals.

17. In a control system for automatically steering an aircraft along anequal intensity path created by radio waves forming partiallyoverlapping radiation patterns in space, automatic pilot means forgyroscopically stabilizing said aircraft on an adjustable heading, radioreceiving means responsive to said radio waves for producing a controlsignal having an amplitude substantially proportional to the differencein intensity of said radiation patterns at said aircraft, meanscontrolling the heading on which said aircraft is stabilized, and meansfor producing a signal substantially proportional to angular deviationof said aircraft from a predetermined heading, said control means beingresponsive to said signals for changing said aircraft heading an amountsuflicient to cause said signals to counteract each other.

18. In a control system for automtaically directing an aircraft along apredetermined line of flight defined by directively radiatedelectromagnetic energy, automatic pilot means for stabilizing thelongitudinal axis of said aircraft at an adjustable pitch angle, radioreceiving means responsive to the intensity of said radiated energy forderiving a pitch signal having an amplitude which is a measure ofdisplacement of said alrcraft from said predetermined line of flight,control means for adjusting said pitch angle, and means for producing asignal substantially proportional to the degree of pitch of saidaircraft from a predetermined pitch angle, said control means being reponsive to said signals for changing said pitch angle an amountsufficient to cause said signals to counteract each other.

19. In a control system for automtaically directing an aircraft along apredetermined line of flight defined by directively radiatedelectromagnetic energy, automatic pilot mean for stabilizing an axis ofsaid aircraft, radio receiving means responsive to the intensity of saidradiated energy for deriving a displacement signal having an amplitudewhich is a measure of displacement of said aircraft from saidpredetermined line of flight, means for deriving a rate signal from saidreceiving means corresponding to the rate of displacement of saidaircraft from said predetermined line of flight, and means actuated bysaid displacement and rate signals for rotating said axis ofstabilization of said aircraft through an angle dependent upon themagnitude of said signals to direct said aircraft back to saidpredetermined line of flight.

20. In a control system for automatically directing an aircraft along apredetermined line or flight defined by directively radiatedelectromagnetic energy, automatic pilot means for stabilizing an axis ofsaid aircraft at an adjustable angle, radio receiving means responsiveto the intensity of said radiated energy for deriving a signal having anamplitude which is a measure of displacement of said aircraft from saidpredeof flight. control means for adthe and means for producing a signalsubproportional to angular deviation of craft axis from a predeterminedangle, trol means being responsive to said lilohanging said anglesuillciently to cause tocounteracteaehother.asystemforsteeringadirigiblecraft an equal intensity path created byrawaves formin partially overlapping radiarng in space, radio receivingmeans reve to said waves for producing a displacet signal having anamplitude dependent upon difference in intensity of said radiation patatsaid craft, means for deriving a rate signal corresponding to the rateof change of said displacement signal, and utilization apparatusresponsive to said displacement and rate signals for determining thecorrective orientation of said craft required for restoring said craftto said path.

22. Apparatus for automatically navigating an aircraft having a turncontrol surface comprisingreceivermeansresponsivetoacourseradiationpattern including means for producing a reversible phase variablemagnitude signal responsive to the relative position of the craft withrespecttosaidcoursepattern andtotherateof change of said relativeposition, a control ampliiler, fed with said signal, a turn motorcontrolled from said amplifier, and automatic pilot means controlledfrom said turn motor, said au- -EEEE egg tomatic mean being connectedfor actuating the turn control surface of said aircraft.

, FRANCIS L. MOSH-HY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,958,259 Becker May 8, 19342,077,401 Crosby Apr. 20, 1937 2,165,800 Koch July 11. 1939 2,190,390Thiry Feb. 13. 1940 1,818,708 Hammond Aug. 11, 1931 2,133,285 DunmoreOct. 18, 1938 2,201,174 Harding et a1. May 21, 1940 1,942,567 WhitmanJan. 9, 1934 2,126,910 Moseley Aug. 16, 1938 2,163,411 Beeley June 20,1939 2,253,508 Crane et al Aug. 26, 1941 2,266,410 Busignies Dec. 16,1941 2,204290 Alkan June 11, 1940 2,137,974 l 'lschel Nov. 22, 19381,730,861 Nottage Oct. 8, 1929 2,315,386 Baldwin Mar, 30, 1943 2,209,826Ogden July 30, 1940 1,339,930 Henderson May 11, 1920 1,061,191 LeonardMay 6, 1913 1,804,126 Stoller May '5, 1931 1,586,233 Anschutz-KaempfeMay 25, 1926 2,300,742 Harrison et a1 Nov. 3, 1942 2,303,654 Newton Dec.1, 1942 2,113,164 Williams Apr. 5, 1938 2,322,225 Crane et al. June 22,1943 maleatwhichsaidaircraftissta Certificate of Correction Patent N 0.2,423,336. July 1, 1947. FRANCIS L. MOSELEY It is hereby certified thaterrors appear in the printed specification of the above numbered patentrequiring correction as follows: Column 16, lines 12 and 13, claim 2,strike out thewords and comma steerin control means, and insert the samein line 11, same claim, after produced, and that the said Letters Patentshould be read with these corrections therein that the same may conformto the record of the case in the Patent Ofiice.

Signed and sealed this 4th day of May, A. D. 194s.

THOMAS F. MURPHY,

Auiatmt flommmioner of Patents.

